Connectors and electronic components are commonly coated with resinous materials for sealing, adhesive or insulative purposes. One important resin material used as a coating in electronic applications is an epoxy polymer. Epoxy polymers are utilized because of their adhesiveness, elastomeric and insulative properties.
Epoxy-amine systems are important in a number of coating applications. Amines act as crosslinkers or curing agents to provide the epoxy-amine polymer with a variety of properties. Epoxy groups react at ambient temperatures with primary aliphatic amines to form secondary amines and with secondary amines to form tertiary amines. Reaction rates depend on epoxy and amine structure and concentration, catalysis, and media effects. Terminal epoxy groups, such as glycidyl ethers and esters, are generally more reactive than internal epoxy groups, which are more sterically hindered. Reactivity of amines tends to increase with base strength and decrease with stearic crowding. Aliphatic amines are much more reactive than aromatic amines, which are much less basic.
The reactivity of currently available epoxy-amine systems limits their uses as a coating for connectors and electronic components. For example, epoxy-amine reactivity is too high at ambient temperatures to allow sufficient storage stability of a coating containing polyamine and polyepoxide in the same package, as a result, two package systems are often required. Aliphatic amines have a pot life limited to a few hours and the coating will generally take about one day to a week to cure at ambient temperatures.
Another factor which limits the use of epoxy-amine systems as a coating for connectors and electronic components is their physical properties. Application of an epoxy-amine composition to a substrate often requires the use of organic solvent to provide suitable viscosities. Organic solvents are objectionable from an environmental standpoint and may have detrimental effects on the substrates to which they are applied. This is especially true when the coating is applied to a substrate supporting conductive ink traces. The use of organic solvents can result in the leaching and migration of metals from the conductive ink on the substrate into the coating, hence, changing the insulative properties of the coating.
Further, epoxy-amines do not provide an optimal adhesiveness or dielectric withstanding voltages to make them an effective coating for use in electronic applications.
Polyamide curing agents for epoxy resins are known in the art. However, the known polyamide curing agents do not cure through the amide group. That is, the hydrogen atom on the nitrogen atom proximate to the carbon atom double bonded to the oxygen atom does not leave the nitrogen to initiate the polymerization of the epoxide. Traditional polyamide curing agents cure through a free amine. That is, the hydrogen on the nitrogen not adjacent to the carbon atom double bonded to the oxygen atom leaves the nitrogen to initiate the polymerization of the epoxide.
It is an object of the present invention to provide an epoxy composition which is cured through an amide hydrogen.
It is an additional object of the present invention to provide an elastomeric epoxy composition that cures rapidly at low temperatures.
It is another object of the invention to provide an elastomeric epoxy composition with an adhesiveness and dielectric withstanding voltage which makes the composition effective for use on electrical connectors and electrical components.
It is a further object of the invention to provide an elastomeric epoxy composition that does not require the use of organic solvent for application to a substrate.
Other objects, advantages, features and characteristics of the present invention will become more apparent upon consideration of the following description and the appended claims.